source should be very small because of the inherent low energy of these secondary particles and the short half-life of most of the isotopes concerned with these processes. 323 EXTRAPOLATION OF BETA ACTIVITIES TO SAMPLING TIME The activities Ag were extrapolated to the sampling time of each intermittent fallout collector tray. The method of extrapolation was determined by the amount of decay data obtained from each shot and varied for each shot. In germeral, the activity consisted of fission activity decay and the decay from uranium capture products. The fission products decayed in a manner which can be represented as; Ap = where Ayt n (3-4) Ayp= Activity when t = 1 Ap = f = n= Activity at later tim Time after shot Decay Exponent The uranium neutron capture products activity decay can be represented best as a sum of individual nuclides which can be determined by radio= chemical analysis. The form of the equation would be; Ay = bool > Cye¥it) where (305) A, = Activity due to capture products at time t Aeo= Proportionality constant such that Ago EC = Aoe where Ace is the zero time activity of the uranium neutron capture activities Czy = relative initial activity of nuclide uj = semi-log decay constant of ith nuclide The ratio of yield of the various uranium neutron capture nuclides can be expected not to vary from sample to sample. This is because they are all uranium isotopes during the time of fallout formation. These ratios (which determine the C,'s) may be found from capture to fission ratios determined by radiochemical meanse The relative amount of the uranium neutron capture activity with respect to the fission activity varies from sample to sample. The values for Ay¢ and n of Eqe 3.4 were found from the decay curve after 2000 hours when the neutron capture activity no longer contributed significantly to the sample activity. The difference between this activity (Eqe 3-4) and the experimentally determined activity at times earlier than 2000 hours was used as a~measure of uranium capture activity. From this the value of Agy (in Eq. 305) could be determined. This difference was measured at the earliest possible time when the difference was greatest. 37